This invention relates to papermaker's wet press felts and more particularly to such a felt in which the opposite ends are joined by a pin seam.
The prior patent art contains numerous examples on pin-seam type felts for paper making machines, along with discussions of the advantages which can be gained by using pin-seam felt over a more conventional endless felt. These prior patents include the following U.S. and foreign patent documents:
Draper, Jr., 2,883,734 of Apr. 28, 1959 PA1 Kelleher, et al, 3,283,388 of Nov. 8, 1966 PA1 Codorniu, 3,815,645 of Jun. 11, 1974 PA1 Cannon, 4,401,137 of Aug. 30, 1983 PA1 Lilja et al, 4,601,785 of Jul. 22, 1986 PA1 Talonen et al, 4,698,250 of Oct. 6, 1987 PA1 Johansson et al, 4,743,482 of May 10, 1988 PA1 Sakuma, 4,755,260 of Jul. 5, 1988 PA1 Japanese Pat. No. 57-55358
Typically, the pin seam felt today is formed with a woven base fabric and carries one or more layers of needled batting material on one or both of the face surfaces of the base fabric. An advantage of the pin seam on such a felt s that the felt can be made as stiff as desired, and still get it threaded onto the paper making machine. If the same felt were woven endless, it would be very heavy, stiff, and difficult to install on the machine.
Difficulties are encountered in two general areas. The one of these difficulties resides in the necessity of threading the pin through the cross-machine fabric loops on the opposed ends of the felt. The ends of the felt must be brought together on the machine, and a flexible leader wire is threaded through the internested loops, a short section or length at a time. Then it is used to pull the pin through while pulling the leader out of a gap between loops. This is repeated across the width of the machine, which may exceed 400 inches. The tedious process is often made all the more difficult because of cramped space and poor lighting.
A second difficulty resides in the necessity of cuting through the layer or layers of needled batting at the pin seam joint, since the joint was temporarily joined during felt manufacture and batt needling. Once the batting layer has been severed at the seam, it is very difficult to join it together again on the machine.